Transcript Chapter 14 Autonomic Nervous System Nerve Cells of the Enteric

Chapter 14
Autonomic
Nervous System
Nerve Cells of the Enteric Plexus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SNS vs. ANS
• Somatic Nervous System (SNS)
– Cell bodies of somatic neurons are located in CNS
– axons extend to skeletal muscles --have an excitatory effect
– Usually controlled consciously
• Autonomic Nervous System (ANS)
– Cell bodies of preganglionic neurons are located in CNS
– axons extend to ganglia where they synapse with postganglionic
neurons
– The postganglionic axons can have an excitatory or inhibitory
effect on
• Smooth muscle
• Cardiac muscle
• Glands
– Usually controlled unconsciously
Fig. 14.1
Tab.
14.1
Anatomy of the Autonomic Nervous System
•
Subdivided into
– Sympathetic division
– Parasympathetic division
– Enteric nervous system
•
Sympathetic and Parasympathetic
divisions differ structurally in
1. Location of preganglionic neuron cell bodies
within CNS
2. Location of autonomic ganglia
The Sympathetic Division
•
•
Preganglionic cell
bodies are in lateral
horns of the spinal cord
gray matter from T1 to
L2
Preganglionic axons
pass through ventral
roots to white rami
communicates to
sympathetic chain
ganglia. From there,
four courses are
possible
Fig. 14.2
The Sympathetic Division
1)
2)
Preganglionic axons synapse (at same or a different level) with
postganglionic neurons, which exit ganglia through gray rami
communicates and enter spinal nerves
Preganglionic axons synapse (at same or a different level) with
postganglionic neurons, which exit ganglia through sympathetic
nerves
Fig. 14.3
The Sympathetic Division
3)
4)
Preganglionic axons pass through chain ganglia without
synapsing to form splanchnic nerves. Preganglionic axons then
synapse with postganglionic neurons in collateral ganglia
Preganglionic axons synapse with cells of adrenal medulla
Fig. 14.3
The Parasympathetic Division
• Preganglionic cell bodies are
in nuclei in brainstem or lateral
parts of spinal cord gray
matter from S2 to S4
– Preganglionic axons from brain
pass to ganglia through cranial
nerves
– Preganglionic axons from sacral
region pass through pelvic
splanchnic nerves to ganglia
• Preganglionic axons pass to
terminal ganglia within wall of,
or near, organ that is
innervated
Fig. 14.4
Tab.
14.2
Enteric Nervous System
•
•
Consists of nerve plexuses within wall of
the digestive tract
Has contributions from 3 sources:
1. Sensory neurons that connect digestive tract
to the CNS
2. ANS motor neurons that connect CNS to
digestive tract
3. Enteric neurons, which are confined to
enteric plexuses
Distribution of Autonomic Nerve Fibers
• Sympathetic, parasympathetic and sensory
neurons intermingle in autonomic nerve
plexuses
• Sympathetic axons reach organs through spinal,
sympathetic, and splanchnic nerves
• Parasympathetic axons reach organs through
cranial and pelvic splanchnic nerves
• Sensory neurons run alongside sympathetic and
parasympathetic neurons within nerves and
nerve plexuses
Fig. 14.5
Neurotransmitters of the ANS
• Acetylcholine is released by cholinergic
neurons
– All preganglionic neurons
– All parasympathetic postganglionic neurons
– Some sympathetic postganglionic neurons
• Norepinephrine (or epinephrine) is
released by adrenergic neurons
– Most sympathetic postganglionic neurons
Receptors of the ANS
• Acetylcholine binds to
– Nicotinic receptors
• Found in all postganglionic neurons
• Excitatory
– Muscarinic receptors
• Found in all parasympathetic effector organs
• Some sympathetic effector organs
• Excitatory or inhibitory
• Norepinephrine and epinephrine bind to
– Alpha and beta receptors
• Found in most sympathetic effector organs
• Excitatory or inhibitory
Fig. 14.6
Tab.
14.3
Regulation of the ANS
• Autonomic reflexes control most of activity of
visceral organs, glands, and blood vessels
• Autonomic reflex activity can be influenced by
hypothalamus and higher brain centers
• The sympathetic and parasympathetic divisions
can influence activities of enteric nervous
system through autonomic reflexes
• The enteric nervous system can function
independently of CNS through local reflexes
Fig. 14.7
Functional Generalizations About the ANS
• Both divisions of the ANS produce stimulatory and
inhibitory effects
• Most organs are innervated by both divisions
– Usually, each division produces an opposite effect on a given
organ
• Either division alone or both working together can
coordinate the activities of different structures
• The sympathetic division produces more generalized
effects than the parasympathetic division
• Sympathetic activity generally prepares the body for
physical activity
• Parasympathetic activity is more important for resting
conditions